Selecting a motor for Perseverance was one of the easier tasks. There are a couple of constraints that are quickly established, namely the voltage (48VDC from batteries) and from hull drag calculations and reading reports of other electric boats. a range of 10-20kW was chosen.
I have always been a slow boater (though I never got to China – get it?). I don’t think I have ever used full power on a boat I have hired, and when sailing I’d rather glide about in a Force 2 than thrash about in a Force 5. That’s fine for canals, but there is always the question of rivers. The simple answer is that there will always be rivers that a narrowboat cannot go up, and I am happy to be a little more restricted in that regard than if I had a bigger motor. Make it 10-15kW.
Motors come in different types, and I ruled out some swiftly:
DC motors with commutators make an annoying noise and need maintenance. Given the criteria that “silence is golden”, and I hate doing routine maintenance, this is not acceptable.
AC induction motors are big and heavy for the power they produce, are less efficient than more modern motors and are old technology.
Permanent Magnet AC (PMAC) motors of various types are suitable, and these can be split into water cooled and air cooled.
Water cooled motors may be quieter, but the overhead in having water cooling circuit with pumps, skin tanks, anti-freeze etc. when it’s not necessary made water cooling an unlikely choice.
- A UK company providing PMAC motors exhibited at the Crick show in 2019, but refused to talk to me when I contacted them.
- Chinese made PMAC motors, of the type often seen on hybrid installations, are limited to 10kW, and look poorly constructed. I have always seen them mounted with belt drives, which again I didnt' want to include.
- Motors supplied by an English company representing a German parent with Dutch motors originating in Italy were not attractive as I was afraid that any technical questions would get lost in translation.
Air Cooled PMAC motors are made by a Croatian company, Tema. They were easy to contact and the very helpful company director is also the designer. Tema motors were already installed in a number of boats including narrowboat Ampere, and Malcolm Bridge, the owner of Ampere, was very complimentary about the motor and so I decided to fit one.
Simple as that. 16 potential motors reduced to one.
For once - a short blog!